This invention relates to fabrication of interface material and structures employing carbon nanotube (CNT) array.
Carbon nanotube is a nano-scale structure of cylindrical carbon molecules. A CNT array is an array of CNTs, and the CNTs may be aligned in a direction.
CNTs have been produced and observed under a variety of conditions. CNTs have many potential applications such as thermal interface material, electromagnetic, chemical, mechanical and electrical. Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, high pressure carbon monoxide (HiPCO), and chemical vapor deposition (CVD). CNTs' electrical conductance is related to their structure and are chemically stable. CNTs typically have very small diameters and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that CNTs will play an important role in fields such as nano-scale integrated circuits, field emission, and single electronic components. Of particular interest are CNTs with all the nanotubes aligned in the same direction. While such a material presents handling difficulties, it has the promise to be a superior thermal conductor.
In thermal management applications, a conventional thermal interface material is obtained by diffusing particles with a high heat conduction coefficient in a base material. The particles can be graphite, boron nitride, silicon oxide, alumina, silver, or other metals. However, the heat conduction coefficient of conventional thermal interface material is considered to be too low for many contemporary applications, because it cannot adequately meet the heat dissipation requirements of modem electronic components.
Physically, the length of a CNT can be several thousand times its diameter, and the tensile strength of CNTs can be one hundred times that of steel. However, the weight of CNTs is only one sixth of that of steel. Furthermore, CNTs have good flexibility and excellent heat conduction coefficients. Thus, CNTs have excellent characteristics for thermal conduction applications.
For example, CNTs arranged with the nanotubes parallel to the direction of heat flow offer a marked improvement in thermal management. An article entitled Unusually High Thermal Conductivity of Carbon Nanotubes and authored by Savas Berber (page 4613, Vol. 84, Physical Review Letters 2000) discloses that a heat conduction coefficient of a CNT can be 6600 W/mK (watts/milliKelvin) at room temperature.
U.S. Pat. No. 6,407,922 discloses a thermal interface material employing CNTs. The thermal interface material is formed by injection molding and has a plurality of CNTs incorporated in a matrix material. A first surface of the thermal interface material engages with an electronic device, and an opposite second surface of the thermal interface material engages with a heat sink. The second surface has a larger area than the first surface, so that heat can be uniformly spread over the larger second surface. However, the thermal interface material is relatively thick and has reduced flexibility. In addition, the CNTs are disposed in the matrix material randomly and multi-directionally. This means that heat does not necessarily spread uniformly through the thermal interface material. Furthermore, heat does not necessarily spread directly from the first surface engaged with the electronic device to the second surface engaged with the heat sink.
U.S. Pat. No. 7,086,451 discloses a heat sink employing CNTs. A layer of CNTs is grown directly on a prepared surface of the heat sink base by catalytic vapor deposition. During the deposition process, the substrate is heated to approximately 700° C. This high temperature can be destructive to some materials and hence limits the choice of material for the heat sink base.
To take full advantage of the properties of CNTs, a capability is desired to use CNTs with aligned tubes and interface the CNTs to a heat sink without having to heat the heat sink to high temperatures. As such, there is a need to develop improved methods to manufacture interface material and structures employing CNTs.